CHAPTER 3. Energy Balance and Temperature
Chapter Overview:
The chapter explores solar radiation as the primary heat source for the atmosphere. The
transparency of gases to insolation and absorption of terrestrial radiations are also examined.
Concepts such as absorption, transmission, or scattering, and reflection are explored, as is the
global energy budget.
Chapter at a Glance:
• Atmospheric Influences on Insolation - Radiant energy incident upon the
Earth-atmosphere system is absorbed, reflected, or transmitted by atmospheric gases
and/or the Earth’s surface. Energy reflected and/or transmitted (scattered in the
atmosphere) does not contribute to heating. Absorbed energy encourages direct heating.
A. Absorption - Particular gases, liquids, and solids in the atmosphere absorb
radiant energy. Heat increases in the absorber while less energy is transferred to the
surface. Although atmospheric gases are rather selective in the wavelengths they
absorb they are overall poor absorbers of energy.
B. Reflection and Scattering - Energy is effectively redirected by objects through
reflection but this process does not increase heat in the reflector, as energy is not
absorbed. However, in most instances, only a portion of incident energy is
reflected from an object. That portion is its albedo. Specular reflection is reflection
of energy as an equally intense energy beam. Energy reflected in such a way as to
disperse energy into many weaker wavelengths is diffuse reflection, or scattering.
The composition of the atmosphere effectively scatters radiation. That energy
which reaches the surface is diffuse radiation and differs in intensity from direct
radiation. Characteristics of scattering are dependent upon the size of the scattering
agents.
1. Rayleigh Scattering - Gases, or other scattering agents smaller than
energy wavelengths, scatter energy forward and backward. <Web>
Because the scattering agents are so small, this Rayleigh scattering is partial
to shorter wavelength energy, such as those which inhabit the shorter
portion of the visible spectrum. Rayleigh scattering is responsible for a blue
sky as beams of solar radiation strike atmospheric gases and are redirected
in all directions. Blue light is among the shortest and most readily scattered
wavelengths by gases so that a blue sky is indicative of a clean, particle free
atmosphere. Backscattering of blue light is also responsible for the Earth’s
bluish tint when viewed from space. At sunrise and sunset, the reddish
atmosphere is also caused by Rayleigh scattering as light passing through a
longer atmospheric trajectory has shorter wavelengths effectively scattered
out, leaving only the longer reddish colors.
2. Mie Scattering - Larger scattering agents such as suspended aerosols
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scatter energy only in a forward manner. <Web> This combined with the
fact that the larger particles interact with wavelengths across the visible
spectrum produces hazy or grayish skies. This Mie scattering also enhances
longer wavelengths during sunrises and sunsets and is indicative of a rather
aerosol laden atmosphere.
3. Nonselective Scattering - Water droplets, which are larger than energy
wavelengths, scatter wavelengths of the visible spectrum equally leading to
a white or gray appearance. Since no wavelength is especially affected, the
scattering is nonselective.
4. Transmission - The percentage of energy transmitted through the
atmosphere to the surface is dependent upon the ability of the atmosphere to
absorb, scatter, and reflect. Thus, transmission of energy varies diurnally
from place to place
• The Fate of Solar Radiation - To understand Earth’s energy balance, global annual
insolation is assumed to be 100 units. <CD2.4> The atmosphere directly absorbs 25 units
with 7 of these absorbed by stratospheric ozone, the rest by gases such as water vapor
absorbing near-infrared wavelengths. Globally, atmospheric reflection averages 25 units,
19 of which are reflected to space by clouds and 6 units which are backscattered to space
from atmospheric gases. The remaining 50 units are available for surface absorption but 5
units are reflected back to space. These 5 units combined with the 25 scattered to space
from the atmosphere equates to a total planetary albedo of 30%. The remaining 45 units of
energy at the Earth’s surface are absorbed, leading to surface warming. Earth processes
eventually transfer this energy from the Earth system back to space. <Web>
• Energy Transfer Processes Between the Surface and the Atmosphere - There is a
continuous exchange of energy between Earth’s surface and the atmosphere. <CD2.4>
A. Surface-Atmosphere Radiation Exchange - Due to Earth’s low temperatures,
terrestrial radiation emitted is primarily of the longwave variety. Much of this,
primarily IR, is absorbed by various atmospheric gases, namely water vapor and
carbon dioxide, and transferred uniformly in the atmosphere. Some is re-absorbed
by the surface, which further heats the atmosphere. Terrestrial wavelengths peak
between 8 and 12 µm, a region of the spectrum not absorbed by atmospheric gases.
These wavelengths pass directly to space with the phenomena termed, the
atmospheric window. <Web> Clouds absorb nearly all terrestrial radiation
accounting for moderated temperatures during their presence. Longwave radiation
balance begins with 104 units (Earth is a constant emitter) where 88 units are
re-directed to the surface to reheat, and 66 are radiated to space. Net radiation is the
difference between that absorbed and that emitted. The atmosphere absorbs 25
units of insolation and loses 54 for a deficit of 29 units. The surface absorbs 45
units but has a net deficit of 16 units of longwave energy, which equates to a net
surplus of 29 units. So, the atmosphere’s net deficit exactly equals the surface
surplus. Energy transfers between the surface and atmosphere and back through the
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processes of conduction and convection. The two processes dissipate surface
energy surpluses and reduce the atmosphere’s energy deficit. <CD2.5>
B. Conduction - Conduction is important in near surface energy transfers,
typically transferring energy from the surface to lower atmospheric depths. The
laminar boundary layer, a very thin surface air layer, heats through conduction
before convection transfers this energy aloft.
C. Convection - Because convection involves molecular displacement, energy is
circulated between the lower atmosphere and that aloft and back again. Two
processes accomplish this, free and forced convection. <Web>
1. Free Convection - Free convection relates to buoyance of a fluid
induced through temperature changes. <CD2.5> <ME3.1>
2. Forced Convection - Forced convection, also called mechanical
turbulence, refers to the turbulent process of large-scale air flow. Friction
and other such interactions break uniform airflow into smaller eddies of
turbulent flow which carries energy aloft and/or downward.
3. Sensible Heat - Sensible heat refers to heat energy, which is readily
detected. The magnitude of heating is related to an object’s specific heat or
the amount of energy needed to change the temperature of an object a
particular amount (J/kg/K). Heating is also related to an objects mass with
higher mass objects requiring more energy for heating. Globally, 8 units of
energy are transferred from the surface to the atmosphere as sensible heat.
4. Latent Heat - Latent heat is energy required to induce changes of state in
a substance. In atmospheric processes, this invariably involves water. Ice
melting requires latent heat of fusion while evaporation involves latent heat
of evaporation. When water is present, latent heat of evaporation redirects
some energy which would be used for sensible heat so that wet
environments are cooler for their insolation amounts than drier ones. Latent
heat of evaporation is stored in water vapor, only to be released as latent
heat of condensation when that change of state is induced. Globally, 21
units of energy are transferred to the atmosphere as latent heat.
D. Net Radiation and Temperature - Earth’s radiation balance is a function of an
incoming and outgoing radiation equilibrium. <CD2.5> If parameters were
changed, a new equilibrium would be achieved. These balances occur on an annual
global scale, and also diurnally over local spatial scales. The balance is best
exemplified by examining radiation and temperature over a cloudless day. Coolest
temperatures occur just after dawn as outgoing radiation is maximized and
incoming radiation is weak. As solar declination improves, temperatures increase
but maximum solar angle (noon) and maximum temperatures (2-4:00pm) are
offset. The diurnal temperature lag is caused by afternoon to evening energy
surpluses in addition to the slower energy transfer mechanisms of conduction,
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convection, and latent heat. Such conditions also occur on a larger-scale resulting
in hemispheric seasonal temperature lags.
E. Latitudinal Variations - Radiation equilibrium varies by latitude such that
areas between 38o N and S run net energy surpluses while poleward positions
experience net deficits. Further, the margin between net gains and net loses of
energy migrates seasonally. For the summer hemisphere, net gains occur poleward
of about 15o. For the winter hemisphere, the situation is reversed. Latitudinal
imbalances are neutralized through mean horizontal mass advection. Such a
situation occurs as energy imbalances create pressure differences, which result in
winds and currents, which transport energy latitudinally.
• The Greenhouse Effect - Trapping terrestrial radiation by certain atmospheric gases is
called the greenhouse effect. The moniker stems from greenhouses, which allow solar
radiation to enter through glass panes but trap outgoing heat energy. Technically, the Earth
process is far different from an actual greenhouse as greenhouses simply stem heat loss
through convection, a regular process in Earth’s atmosphere. So the name is misleading.
Without atmospheric gases trapping outgoing terrestrial radiation, average Earth
temperatures would be about -18oC (0oF). So the process is vital to maintaining current,
habitable Earth temperatures. Increases in greenhouse gas concentrations may lead to
future climatic changes. <Web>
• Global Temperature Distributions - Globally illustrated isotherms depict both the
general decline of temperatures poleward and the fact that the strongest latitudinal thermal
contrasts occur in the winter hemisphere. Hemispheric energy surpluses account for a
smaller latitudinal thermal gradient during summer. Also noticeable is a summertime
poleward and a wintertime equatorward shift in isotherms over continents documenting the
quick heating and cooling of land surfaces as opposed to water surfaces. Lastly, N.H.
thermal gradients are more pronounced than in the S.H. due to greater landmass.
• Influences on Temperature - Many factors combine to influence spatial temperature
patterns.
A. Latitude - Mean annual temperatures decrease with increasing latitude. This is
due to lower solar angles with increasing latitude as well as the influence of the
Earth’s axial tilt. Low latitudes enjoy high solar angles and similar lengths of
daylight all year. With increasingly high latitude come exacerbated insolation
extremes as day length shifts seasonally.
B. Altitude - Tropospheric temperatures typically decrease with increasing altitude
as the surface accounts for the majority of available energy to the atmosphere.
Since higher altitudes are farther removed from the source of heat, temperatures
decrease. Overall, temperatures at high altitudes remain fairly constant in relation
to air near the surface. Similarly, air at high elevations (but near a surface)
undergoes more rapid diurnal temperature fluxes than air at lower elevations and/or
air at a similar altitude but above the surface.
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C. Atmospheric Circulation - Latitudinal temperature, and therefore pressure,
differences cause large-scale horizontal energy transport through advection.
Advection also influences latitudinal moisture regimes and, consequently, cloud
cover which also impacts temperatures.
D. Contrasts Between Land and Water - Surface composition directly influences
atmospheric heating. Water bodies heat slower than land given approximate
insolation amounts. Continentality is the exacerbation of seasonal temperature
extremes experienced by continental interiors. Maritime locations experience more
moderate seasonal temperatures as water bodies heat less than land due to a higher
specific heat, transparency to energy, continual cooling through evaporation, and
horizontal and vertical mixing through currents.
E. Warm and Cold Ocean Currents - Due to ocean-atmosphere circulation
coupling, western ocean basins experience warm ocean currents while eastern
basin portions maintain cold ocean currents. Coastal air temperatures are greatly
influenced by these currents as the surface temperature largely controls the amount
of energy transfer to the atmosphere. This combined with general atmospheric
circulation ensures that west coast mid-latitude locations experience more
moderate seasonal temperatures than east coast mid-latitude locations.
<ME3.2;3.3>
F. Local Impacts on Temperature - Many small spatial scale features impact
temperatures. Equatorward facing slopes received more direct solar angles than
slopes of other directions causing greater energy absorption and heating. This often
leads to greater evaporation and overall drying. Also, forested regions reduce
surface insolation during the day and trap radiation at night leading to cooler
daytime and warmer nighttime temperatures.
• Measurement of Temperature - Either mercury or alcohol based thermometers are used
to record temperatures. A maximum thermometer is used to record the daily maximum
temperature while a minimum thermometer is used to record the minimum temperature.
Bimetallic strips are used in conjunction with a rotating recording device to produce a
thermograph which givens continuous temperature records. Thermistors are fast-response
temperature recording devices based on resistance to electrical current and are mainly used
in radiosondes.
A. Instrument Shelters - Vented weather shelters are necessary to accurately
gauge air temperature as direct exposure of a thermometer causes energy
absorption by the thermometer. Weather shelters are also painted white to increase
albedo and reduce direct insolation gains. A shelter must also be five feet above
ground so as not to be overly biased by laminar layer heating.
• Temperature Means and Ranges - A standard averaging procedure is used to obtain
daily mean temperatures as all averaging methods bias a sum in some manner. The daily
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mean is a simple average of the maximum and minimum diurnal temperature. Because
surface heating occurs rapidly during the afternoon hours, this method introduces a bias
toward higher daily temperatures over averaging 24 hourly temperatures. However, this is
the accepted method. A daily temperature range is calculated by simply subtracting the
daily minimum from the daily maximum. Monthly mean temperatures are found through
summing all daily means and dividing by the total number of days. Annual mean
temperatures are similarly calculated as the sum of all monthly means and are divided by
the number of months.
A. Global Extremes - Due to continentality the greatest extreme temperatures ever
recorded occur at continental interior locations. A world record high temperature
of 57oC (136oF) was recorded at Azizia, Libya in 1913, while the world’s lowest
temperature, -89oC (-129oF), was recorded in Antarctica in 1960.
• Temperature and Human Comfort - Temperature may exert major impact on human
discomfort, but this is particularly exacerbated by other weather factors such as wind and
humidity. Wind causes an increase in sensible heat loss from the body. High winds and
cold conditions combine to create a colder condition than if no wind were present. The
wind chill temperature index quantifies the relationship between wind speed and
temperature. A new formula is now used which decreases the effect of wind on human
comfort. Conditions such as exposure to direct sunlight, however, are not directly
considered by the new formula. High humidity combined with high temperatures cause
conditions which seem oppressively hot. A heat index incorporates the combination of
these two weather variables.
• Thermodynamic Diagrams and Vertical Temperature Profiles - Temperatures vary
both horizontally and vertically through the atmosphere. Rapid temperature decreases with
height increase the potential for cloud development and even severe thunderstorms.
Temperature inversions suppress atmospheric mixing which leads to surface pollution.
Thermodynamic diagrams depict the vertical profile of temperature and humidity with
height. This information is integral to the development of accurate forecasts. Upper air
data are obtained through the use of radiosondes carried aloft by weather balloons twice
daily. The easiest thermodynamic diagram is the Stuve diagram which plots temperatures
as a function of the pressure level. The temperature plotting, or sounding, conveys critical
information used in forecasting applications.
Chapter Boxes:
3-1 Physical Principles: Selective Absorption by Water Vapor and Carbon Dioxide Water vapor and carbon dioxide are the two most important absorbers of terrestrial
radiation. Gas molecules only absorb photons of particular energy states. Water vapor and
carbon dioxide are selective in that they are transparent to shortwave energy but nearly
opaque to certain long wavelengths. <Web> Solids and liquids are not similarly selective
absorbers.
3-2 Physical Principles: Earth’s Equilibrium Temperature - Using energy budget
equations for an Earth with no atmosphere, it is evident that such a condition would
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promote temperatures far below those now. The atmosphere is, therefore, essential to a
warm planet. Computer models try to emulate the current atmosphere but due to the
complexity of the atmosphere, realistic models are quite simplistic. However, they are
essential to understanding and forecasting aspects of weather and climate.
3-3 Special Interest: Recent Severe Heat Waves - Recent killer heat waves affected
much of the eastern US during the summers of 1995 and 1999. A combination of high
temperatures and high humidity led to apparent temperatures between 39.4 and 47oC
(103-117oF). This led to high mortality rates in many areas, most notably Chicago, IL.
3-4 Forecasting: Effects of Cloud Cover and Wind Speed on Temperature - Cloud
cover and wind speed are valuable indicators for predicting maximum and minimum
temperatures. Cloud cover reduces the amount of solar radiation received at the surface
causing a decrease in maximum daytime temperatures. Overcast conditions at night reduce
longwave radiation loss keeping minimum temperatures higher than otherwise. Strong
winds also moderate daily temperature ranges a they promote greater forced turbulence.
This augments heat transfer aloft which reduces maximum temperatures. This process also
works to reduce the rate of surface cooling as air will not be in contact with the chilled
surface long enough to be chilled.
CD Rom Unit 2 - Global Energy Balance:
1. Introduction - The Unit 2 Tutorial begins by describing the continuous input of solar
radiation to the Earth-atmosphere system. Input is offset by continual loses of terrestrial
radiation emitted to space. Because positive amounts of energy occur at the surface, a
continual transformation of energy from one form to another allows an energy balance.
2. Radiation - Objects above absolute zero (0 K) emit radiation with the quantity and
quality of emitted radiation determined by the temperature of the emitter. This radiation is
emitted as waves with electric and magnetic perpendicular components. A graphic
illustrates wave propagation. Graphics show that the amount (quantity) of energy is
proportional to wave amplitude while the type (quality) is related to wavelength. The
graphics also compare short and long wavelengths and wave amplitudes. An interactive
animation allows comparisons between different stars (with different temperatures) and
radiation intensity. This reiterates that as temperature increases, energy is emitted at
shorter wavelengths.
Because of the items discussed above, the Sun produces 99% of its energy as short wave
energy; below 4 µm. Graphics of shortwave radiation interacting with the atmosphere are
provided.
Long wave components are also discussed as the Earth emits virtually all energy above 4
µm. Graphics demonstrate terrestrial radiation emitted and related concepts.
These concepts are explored in the Chapter 2 (Radiation Quantity and Quality and
Intensity and Wavelengths of Emitted Radiation) and Chapter 3 (The Fate of Solar
Radiation) and could be used to augment those areas.
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3. Convective Fluxes - Heat is transferred from the surface to the atmosphere primarily
through convection. An animation depicts warm air rising, demonstrating the transference
of energy aloft. The animations also restate the concepts of sensible and latent heat
transfers. These concepts are discussed in the convection section of Chapter 3.
4. Energy Balance Concepts - A graphic is shown which depicts the concept of thermal
equilibrium, an object maintaining a constant temperature. Another graphic portrays an
object exchanging energy with its environment. Thermal equilibrium remains if energy
losses equal energy gains. Animations recapitulate these concepts. Further animations
extrapolate to a global scale. Emphasis is placed upon total insolation gained being offset
by long wave emission and convective fluxes.
5. Achieving Global Balance - In the presence of no net climate change, the surface,
atmosphere, and planet as a whole must maintain thermal equilibrium. Interactive
graphics allow changing temperatures to note various adjustments in the energy balance.
Results indicate that gains in energy absorbed are offset by emission to promote naturally
occurring thermal equilibrium. Also, the concept that “extra” energy emission occurs at
the surface in addition to the amount of energy gained solely from the Sun. Such a
concept forms the basis of the greenhouse effect.
Related Web Sites:
Convection: www.arts.ouc.bc.cal/geog/G111/6ilong.html
Mie Scattering: http://covis2.atmos.uiuc.edu/guide/optics/mie-scat.html
Rayleigh Scattering: www.vislab.usyd.edu.au/vislab/photonics/fibres/fizzz/scattering2.html
Solar Radiation: http://spencer.thmech.nottingham.ac.uk/~etzjgw/sun.html
Greenhouse Effect: www.co2science.org
Atmospheric Window: www.crseo.ucsb.edu/geos/11121.html
Media Enrichment:
ME3.1 - Movie depicting major thunderstorm development over Florida.
ME3.2 - A climatology of global sea surface temperatures.
ME3.3 - A companion movie to 3.2, depicting actual SSTs from Nov. 1998 to Nov. 1999.
ME3.4 - Pacific Ocean currents. A weather image.
Key Terms:
absorption
planetary albedo
atmospheric window specific heat
albedo
net longwave radiation
specular reflection
net radiation
laminar
boundary layer
direct radiation
inversion
Rayleigh scattering forced convection
Mie Scattering mechanical turbulence
nonselective scattering
wind chill temperature index
sensible heat
reflection
bimetallic strip
free convection
latent heat
thermograph
advection
diffuse reflection
greenhouse effect
thermistor
thermodynamic diagram
continentality
Stuve
maximum thermometer
minimum thermometer
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Review Questions:
1. Explain how the absorption and scattering of radiation in the atmosphere affects the receipt of
solar radiation at the surface.
Particulates suspended in the atmosphere serve to reduce the amount of radiation reaching
the surface. This is accomplished by absorption, reflection, and/or transmission of
available energy by the suspended aerosols.
2. Which two gases are most effective at absorbing longwave radiation?
Water vapor and carbon dioxide are the primary longwave absorbers in the atmosphere.
3. How do specular reflection and diffuse reflection differ?
Specular reflection is reflection of energy as an equally intense energy beam. Diffuse
reflection reflects energy in such a way as to disperse that energy into many weaker
wavelengths. This is scattering.
4. What does the term albedo mean?
Albedo refers to the percentage of reflectivity of an object. High (low) albedo relates to
light (dark) colored objects which reflect a high (low) percentage of energy.
5. What characteristics of Rayleigh scattering cause it to create a blue sky?
Rayleigh scattering scatters energy forward and backward by scattering agents which are
smaller than the energy wavelengths. As such, shorter wavelengths are favored, or
scattered more than longer ones. A blue sky results as blue resides is primary short
wavelength of energy along the visible spectrum.
6. What properties of Mie scattering distinguish it from Rayleigh scattering?
Rayleigh scattering refers to the scattering of energy by objects smaller than the
wavelength of radiation. This is done mainly by atmospheric gases. Because the scattering
agents are so small there is a scattering bias toward shorter wavelengths.
Mie scattering primarily involves suspended particulates which are much larger than gases.
These particulates scatter energy in a forward manner resulting in gray skies when large
amounts of particulates are present.
7. Why are overcast days typically gray?
Mie scattering causes energy scattering in a forward manner resulting in gray skies when
large amounts of particulates are present. Also, nonselective scattering involves equal
scattering of visible wavelengths by large objects such as water drops. This normally
produces a white cloud. However, when large amounts of cloud are present, energy
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becomes depleted through the cloud leaving a grayish cloud overhead (or in extreme cases,
a very dark cloud base).
8. What is the numerical value of Earth’s planetary albedo?
30%
9. Which type of scattering accounts for the majority of Earth’s planetary albedo?
Rayleigh scattering.
10. Describe quantitatively how much solar radiation is absorbed and reflected by Earth’s
atmosphere and surface.
About thirty percent of incoming solar radiation is directly reflected by Earth’s albedo.
About one half of the solar radiation available at the top of the atmosphere actually reaches
the Earth’s surface (about 45%). The remainder is either directly absorbed or reflected by
the atmosphere and objects suspended in the atmosphere.
11. What is the atmospheric window?
The place where the space shuttle enters the atmosphere - just kidding. Terrestrial
radiation peaks between 8 and 12 µm a region of the spectrum not absorbed by atmospheric
gases. These wavelengths pass directly to space with the phenomena termed the
“atmospheric window”.
12. Why is it incorrect to state that longwave radiation bounces back and forth between clouds and
the surface?
Longwave radiation is actually absorbed by clouds which then re-radiate the energy back
towards the surface where it is absorbed again.
13. Explain why the incoming and outgoing radiation for the Earth system (radiation entering and
leaving the top of the atmosphere) must be equal to each other?
Earth’s energy balance exists due to a variety of physical processes that counterbalance.
Thus, equilibrium exists between incoming and outgoing radiation. Changing the
parameters of one will eventually offset the other until a new equilibrium is achieved.
Proof of this balance is that global temperatures remain within a particular threshold
through time. An out of balance system would result in dramatic global temperature
fluxes.
14. How do conduction and convection work together to transfer heat upward?
There is a continual exchange of radiation between the Earth’s surface and the atmosphere.
Conduction transfers energy near the surface, both downward into the surface and upward
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to the laminar boundary layer. Convection transfers energy through the atmosphere
through free and/or forced convection processes. Through these two processes, Earth is
constantly transmitting longwave radiation into the atmosphere while solar insolation is
directly absorbed at the surface.
15. What is the difference between free convection and forced convection?
Free convection relates to the buoyancy of a fluid induced by a temperature induced
temperature change. Forced convection refers to the turbulent process of large-scale air
flow. Friction and other such interactions break uniform airflow into smaller eddies of
turbulent flow which moves energy vertically.
16. Describe sensible and latent heat.
Sensible heat is heat energy that is readily detected. This relates to an object’s specific heat
and mass. Latent heat is energy required to induce changes of state in a substance. Latent
heat of evaporation is energy stored in water vapor. This energy is released to the
atmosphere upon condensation.
17. How do the net input and output of radiation vary with latitude?
Areas between 38o N and S experience net energy surpluses while poleward positions
experience net deficits. However, the margin between net gains and loses migrates
seasonally. For the summer (winter) hemisphere, net gains (loses) occur poleward of about
15o.
18. Which two processes transport energy from zones of radiation surplus to zones of radiation
deficit?
Temperature inequalities create atmospheric pressure differences which cause winds and
currents which transport energy latitudinally.
19. Why does the term greenhouse effect inaccurately describe how the atmosphere is heated?
A greenhouse stems heat loss by limiting convection, a regular process in earth’s
atmosphere. So the name is misleading.
20. Discuss how geographic factors such as latitude and altitude influence the distribution of
temperature across Earth’s surface.
Low latitude locations experience only small temperature changes through the year as
these locations receive nearly constant amounts of solar radiation. Locations farther
poleward experience larger annual temperature ranges as solar radiation values flux due to
Earth-Sun geometry. Because temperatures typically decrease with increasing altitude in
the troposphere, higher altitude locations are typically cooler than lower altitude locations.
However, because altitude refers to height above mean sea level without considering the
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elevation of landmasses below, this may be misleading. In sum, locations far above
Earth’s surface experience minimal fluxes in temperature as compared to locations directly
below, and nearer, the Earth’s surface.
21. How do various instruments used to observe temperature work?
Most thermometers rely upon the principal that fluids expand and contract with changes in
temperature. Bimetallic strips rely on strips of different metals expanding and contracting
accordingly with temperature changes. Thermistor’s utilize the resistance of air to an
electrical current to determine air temperatures.
22. Explain how daily, monthly, and annual mean temperatures are computed from observed
temperatures. Discuss some of the factors that can bias resulting values.
Observation biases accompany the method of calculating daily temperature averages.
Averaging the maximum and minimum daily values may derive a number different from
the number obtained by averaging 24 hourly observations. Once a bias is introduced at the
daily level, it will magnify through other mean values as the daily values are inherently
used to calculate monthly (average of daily means) and annual (average of monthly means)
means.
23. Describe the horizontal and vertical scales on Stuve diagrams.
The horizontal scale of a Stuve diagram depicts air temperature. The vertical scale depicts
pressure in mb. This allows plotting of temperature as a function of the pressure level, not
the height above the surface, which allows a more direct application of meteorological
laws than other diagrams.
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